A study described in the journal Pediatrics finds seven in ten American children don't get enough vitamin D. One in ten has levels so low that they're deficient.

Milk and fish are big sources of vitamin D but so is sunshine -- and that's where researchers think American children fall short:

"Four hours a day of using computers, watching TV or playing video games, they were a 60 percent higher risk of having vitamin D deficiency," said Michal Melamed of the Albert Einstein College of Medicine.

Jasmine Carter, 12, can't drink milk, so she looks for vitamin D elsewhere.

“I get it from yogurt, anything that has milk in it -- I don't really drink milk -- or sometimes I go out in the sun and I play around with my friends," said Jasmine.

It's a big issue for people with dark skin because their bodies can't absorb vitamin D as easily. The Pediatrics study found six in ten African-American teenage girls are vitamin D deficient. Later in life, that can lead to osteoporosis, cancer and, according to another new study, heart problems.

"Two times the risk of high blood pressure, two times the risk of having high blood sugar or blood glucose concentrations and about four times the risk of the metabolic syndrome," said Jared Reis of the National Heart, Lung and Blood Institute.

All of those problems are risk factors for heart disease but can be reduced for most people with just 10-15 minutes of sunshine every day. That's exposure without sunscreen, which of course raises concerns about skin cancer. Researchers advise parents to let kids play outside just a few minutes, then apply sunscreen, to protect against both conditions.